1. Field of the Invention
The present invention relates to a power plant provided with a gas turbine, which uses a low-heating-value gas, such as blast furnace gas (BFG), as a fuel, and a fuel gas cooler that cools fuel gas pressurized in a fuel gas compressor and re-circulated.
2. Description of Related Art
Known power plants provided with a gas turbine, which uses a low-heating-value gas, such as blast furnace gas (BFG), as a fuel, and a fuel gas cooler that cools fuel gas pressurized in a fuel gas compressor and re-circulated include, for example, that disclosed in FIG. 1 in Japanese Unexamined Patent Application, Publication No. Hei 9-79046.
In the case where the power plant disclosed in FIG. 1 of the above-mentioned Japanese Unexamined Patent Application, Publication No. Hei 9-79046 is used in a location where the temperature of the fuel gas can become 5° C. or lower, such as a cold region etc., there is a risk that ice may be formed on a dust collector (dust collection device) 5, causing abnormal discharge of the dust collector 5, and that the ice formed on the dust collector 5 may be scattered toward a fuel gas compressor 6 located downstream, which may damage blades of the fuel gas compressor 6. Therefore, if the power plant disclosed in FIG. 1 of the above-mentioned Japanese Unexamined Patent Application, Publication No. Hei 9-79046 is used in a location where the outside temperature can become 5° C. or lower, such as a cold region etc., the fuel gas that has passed through a fuel gas cooler 16 is supplied to an intermediate position in piping (fuel gas supply system) that guides the fuel gas, which has been mixed and adjusted in a mixing chamber 4 so as to have a suitable heating value, to the dust collector 5, thereby intentionally increasing the temperature of (heating) the fuel gas flowing through the piping.
However, if the gas turbine is operated at the rated output, only a small amount of fuel gas is bypassed to the fuel gas cooler 16. Therefore, in such a case, there has been a problem in that the power generation level is limited because it is required to forcedly reduce the output of the gas turbine (i.e., the power generation level) to generate the fuel gas that is to be bypassed to the fuel gas cooler 16, thereby increasing the temperature of (heating) the fuel gas that is passing through the piping with the fuel gas supplied from the fuel gas cooler 16.